Sep. 26, 2011

Beckett has been wanting to do some more 'hands-on' experiments, so we decided to revisit two classics and talk about properties of matter. Beckett's friend Ian came over to help out. We recently talked about mass, weight, and density, and we've talked about gravity and energy. But now we (mostly me) were wading into unknown territory.

When I was Beckett's age, we learned that there were three states of matter: solid, liquid, and gas. In addition to solid, liquid, and gas, you can now add Maxwell Solids -- also occasionally called Maxwell Liquids or Maxwell Materials. Or how about non-Newtonian Liquids? Now there are so many states of matter that I won't even bother to list them here -- states of matter I've never even heard of and will probably never even see. Bose-Einstein Condensate, liquid crystal, superfluid, plasma... There are many different ways for matter to exist, many states that atoms can occupy depending mostly on their energy levels and levels of organization. So many states, so confusing! But using common household materials we made two different compounds with some very unusual properties.

We started with Oobleck, which is super easy to make, but loads of fun in the kitchen. All you need is a couple of cups of water and a box or two of cornstarch. You add them both to a bowl and stir. Oh, and pay attention as you stir, because the mixture quickly turns into something unusual with fairly unusual properties:

Oobleck is a colloid, which is a mixture in which one substance is microscopically dispersed evenly throughout another substance. Technically, oobleck is a hydrocolloid -- like Jello -- and oobleck and Jello share some properties of both liquids and solids. Oobleck displays what scientists call time-independent viscosity. Take beach sand (and quicksand) for example: if you stand just at the water line, you will slowly sink into the sand, but if you jump up and down, the water and sand will stress around the pressure points where your feet land and will feel very solid. In the video, you can see Beckett and Ian pounding on the oobleck as if it were solid.

Next, we decided to make flubber, a.k.a. silly putty. You can make this using scales and beakers and very careful measurements, or you can just play with the ingredients -- it is hard not to make flubber turn out well! You will need a box of Borax (sodium borate also known as sodium tetraborate, available at most grocery stores in the soap section) and a bottle of white glue. Start by mixing a the sodium borate to a solution of 3-4 percent -- the water quickly super-saturates and won't hold much more unless you use really hot water. Use room temperature water and you'll be fine. Next you want to dilute the glue to an 80 percent solution -- add four parts of glue to one part water and stir well. Finally, combine the sodium borate solution and the glue solution and stir well -- pay attention as you stir because the chemical reaction will begin immediately:

Like oobleck, flubber has some very unusual properties that make it act at times like both a solid and a liquid. Many of the non classical states of matter have what is known as thixotropic properties. Thixotropic will be the word of the day -- it comes from Ancient Greek and means that it changes when handled. An easy way to remember the word is to think of ketchup, and how thick it is. Ketchup is another colloid, a hydrocolloid like oobleck, and, more importantly, it is another non-Newtonian fluid. Turn a ketchup bottle upside down and the ketchup usually sticks to the walls of the bottle. Whack it a couple of times and it sticks even more! Why? Because whacking the ketchup bottle changes the ketchup's viscoelastic properties, increasing the viscosity (thickness) and making it less likely to flow out of the bottle. Don't whack the bottle for a few seconds and the ketchup will act like a liquid again and eventually slowly flow out of the bottle.

Flubber and oobleck will flatten and flow like a liquid if you leave them alone long enough, but roll either into a ball and the ball will bounce quite well. You can also tear flubber and oobleck -- they will actually break into pieces just as solids do.

Now, back to all those crazy states of matter that only exist in very special conditions. Start looking around your house or school and see how many different non-Newtonian liquids you can find. We now know that ketchup is a hydrocolloid and a non-Newtonian fluid, but what about mustard? And sure, Jell-o is wacky and it is easy to see that it possesses the properties of both solids and liquids, but what about puddings? Yogurts? And back to my first list -- you won't find any Bose-Einstein Condensate around your house unless you happen to have the coldest freezer on earth, but what about liquid crystals? Plasma? You might be surprised what kind of states of matter that you can find.

Next week will answer that classic age old science question of what makes the sky blue. As an added bonus, we will answer the question what makes eyes blue-you might be surprised at the answer!